This invention is generally directed to toner compositions, and more specifically the present invention is directed to positively charged developer compositions, including magnetic, and colored developer compositions containing certain charge enhancing additives. In one important embodiment of the present invention, the charge enhancing additives are formulated by the chemical modification and/or chemical adsorption of known additives onto the surface of various flow aid compositions, inclusive of colloidal silicas, and small particle size alumina such as aluminum oxide. Developer compositions with the modified charge enhancing additives of the present invention are useful for causing the development of electrostatic latent images including color images. More specifically, positively charged toner compositions containing the aforementioned modified charge enhancing additives are particularly useful in electrostatographic imaging systems having incorporated therein a silicone fuser roll or a Viton coated fuse roll since these additives can be employed in small quantities and do not react substantially with Viton or silicone causing undesirable decomposition thereof, which adversely affects image quality and service life of the fuser roll. Also, compositions with the chemically treated additives of the present invention possess improved admix characteristics, and enable colored toner compositions with rapid charge exchange. Additionally, the modified additives selected for the toner and developer compositions of the present invention generally possess a large surface area, that is in some instances of about 50 to 400 m.sup.2 per gram; and are of a small particle size with a diameter of, for example, about 7 to about 200 nanometers enabling the particles to easily acquire positive triboelectric charges on contact with the appropriate carrier particles. In addition, the aforementioned flow aids, especially the colloidal silicas, are of low cost and are readily available. Furthermore, the modified charge enhancing additives of the present invention are primarily white in color, and thus will not effect to any extent the coloration of the final toner composition. In addition, the aforementioned modified charge control additives in most instances do not melt upon fusion of the toner, and can in some embodiments permit nonglossy images on paper after fixing. Moreover, the surfaces of the flow aids, especially the silicas, contain thereon acidic silanol groups which are polar enabling the chemical reaction thereof with various bases, including amines, amino alcohol derivatives and compounds which are reactive with hydroxyl groups. Additionally, toner formulations with the charge enhancing additives of the present invention have substantially no adverse blocking characteristics, increased flowability, and they can be selected as magnetic toners without affecting the magnetic properties thereof.
Developer compositions containing charge enhancing additives, especially additives which impart a positive charge to the toner resin are well know. Thus, for example, there is described in U.S. Pat. No. 3,893,935 the use of certain quaternary ammonium salts as charge control agents for electrostatic toner compositions. There is also described in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica. According to the disclosure of this patent, the development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition having a positively charged triboelectric relationship with respect to the colloidal silica. Further, there are disclosed in U.S. Pat. No. 4,338,390 developer and toner compositions having incorporated therein as charge enhancing additives organic sulfate and sulfonate compositions.
Other patents disclosing positively charged toner compositions with charge enhancing additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014; and 4,394,430. Additionally, there are disclosed in Japanese Patent Publication No. 154942 developer compositions having incorporated therein micropowders of silicates treated with aziridines derivatives. Further, in Japanese Patent Publication No. 59-137305 there is disclosed for incorporation into toner compositions silica treated with hydroxy ethylene amine followed by a silane treatment to obtain a hydrophobic material. Furthermore, the preparation of hydrophobic silanes by a silation process is illustrated in German Patent Publication DE No. 3330380. Other prior art includes Japanese Patent Publication No. 57079952 which discloses a positively charged control agent containing silicate micropowder treated with aziridine; Japanese Patent Publication No. 7078-556 wherein there is disclosed a positive charge control agent containing a silicate micropolymer treated with one or more aziridines; Japanese Patent Publication No. 55136-84 which discloses an electrostatic latent image developer containing a charge control agent which may be comprised of microparticles of colloidal silica that can be present in a monoazo dye complex, reference FIGS. 1 and 2; and Japanese No. 57078-550 wherein there is described a developer containing a silicate micropowder as a positive charge control agent.
Additionally, there is illustrated in copending application Ser. No. 891,836, entitled Toner Compositions With Modified Charge Enhancing Additives, the disclosure of which is totally incorporated herein by reference, an improved toner composition comprised of resin particles, pigment particles, and present on the surface thereof additives comprised of a charge enhancing component sorbed on a flow aid composition.
Moreover, there is disclosed in U.S. Pat. No. 4,298,672 positively charged toner compositions containing resin particles and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds, inclusive of cetyl pyridinium chloride. While the developer compositions disclosed in the U.S. Pat. No. 4,298,672 are sufficient for their intended purposes, it appears that the alkyl pyridinium compounds involved react with the polymer coated on Viton fuser rolls causing decomposition thereof. Also, several of the other charge control agents disclosed in the prior art interact with certain fuser rolls, such as Viton fuser rolls, used in electrostatographic systems. This interaction causes the fuser roll to be adversely affected resulting in deterioration of the image quality. For example, Viton fuser rolls discolor and turn black, develop multiple surface cracks and harden when certain charge control additive compounds are contained in the toner mixture.
A Viton fuser roll selected for use in electrostatographic copying machines is comprised of a soft roll fabricated from lead oxide, and duPont Viton E-430 resin, a copolymer of a vinylidene fluoride, and hexafluoropropylene. This roll contains approximately 15 parts of lead oxide, and 100 parts of Viton E-430, which mixture is blended and cured on the roll substrate at elevated temperatures. Presently, the function of the lead oxide is to generate some unsaturation by dehydrofluorination for crosslinking, and to provide release mechanisms for the toner composition. Excellent image quality has been obtained with Viton fuser rolls, however, in some instances there results a toner fuser compatibility problem when unstable charge control agents are part of the toner mixture. For example, it appears that certain specific charge control additives, such as quaternary ammonium compounds and alkyl pyridinium compounds, including cetyl pyridinium chloride, react with the Viton of the Viton fuser roll. For example, cetyl pyridinium chloride, when part of the toner mixture, appears to be catalytically decomposed by the lead oxide contained in the fuser resulting in a highly unsaturated compound, which polymerizes and condenses with the unsaturated Viton E- 430 material. In view of this, the Viton fuser roll turns black, develops multiple surface cracks, and the surface thereof hardens thereby resulting in image quality deterioration. Therefore, there remains a need for affecting the reduction of the amount of chemically and thermally unstable charge enhancing additives in toner formulations, which is achieved with the invention of the present application.
Toner compositions containing many of the above described charge enhancing additives are useful for causing the development of images formed on single, or layered photoresponsive imaging devices comprised of generating layers and transport layers thereby requiring a toner composition that is positively charged in order that the toner particles may be suitably attracted to the electrostatic latent image contained on the photoreceptor surface. These devices usually are charged negatively rather than positively as is the situation with selenium photoreceptors. Thus, efforts have been devoted to obtaining developer compositions containing toner resins which are positively charged. Thus, while many charge control additives are known, there continues to be a need for new additives. Specifically, there continues to be a need for additives which will minimize the interaction with Viton type fuser rolls. Additionally, there continues to be a need for charge control additives which are thermally stable at high temperatures. Moreover, there continues to be a need for positively charged toner and developer compositions with rapid admix charging characteristics. Also, there continues to be a need for new charge enhancing additives, particularly those additives which can be economically prepared. Additionally, there is a need for additives which, in addition to being thermally stable, are substantially nontoxic. In addition, there is a need for efficient charge control additives which can be deposited on small particle surfaces to enable an enhancement of the charge transfer efficiency for the toner compositions selected. Further, there is a need for charge enhancing additives which can be easily and permanently dispersed in toner resin particles. Moreover, there is a need for colored toner compositions which contain positively charged particles, and wherein the resulting toner compositions have desirable toner admix charging, and narrow charge distribution values on the aforementioned compositions. There is also a need for toner compositions which can be selected for the development of colored images in electrophotographic imaging processes wherein there is utilized a minimum amount of charge enhancing additives. Additionally, there continues to be a need for toner and developer compositions wherein, subsequent to development, there results nonglossy colored images on paper or other substrates.